1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a Blade Outer Air Seal (BOAS) segment for a gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
A Blade Outer Air Seal (BOAS) or ring segment is used to form a seal with tips of rotating blades. FIG. 1 shows a prior art BOAS 11 secured by forward and aft hooks to a forward isolation ring 16 and an aft isolation ring 12. The isolation rings 16 and 12 fit within annular grooves formed within a blade ring carrier 13. The BOAS is formed from segments that form an annular arrangement around the blade tips 17. A stator vane 18 is located forward of the blade 17.
Cooling air for the BOAS 11 is provided through cooling air supply holes 14 formed in the blade ring carrier 13 and flows into a chamber above an impingement tube 15 that has an arrangement of impingement cooling air holes spaced around to direct impingement cooling air onto a backside surface of the BOAS. The cooling air then flows through metering holes 19 spaced around the BOAS and into axial direction cooling air holes to provide convection cooling to the hot surface of the BOAS. The cooling air is then discharged out through exit holes 20 arranged along the aft mate face edge of the BOAS 11. FIG. 2 shows an isometric view from the mate face side with the axial cooling holes opening onto the edge.